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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH 0/3] kasan: memorize and print call_rcu stack
Date:   Wed, 6 May 2020 01:53:31 -0400
Message-Id: <2BF68E83-4611-48B2-A57F-196236399219@lca.pw>
References: <20200506051853.14380-1-walter-zh.wu@mediatek.com>
Cc:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        wsd_upstream <wsd_upstream@mediatek.com>,
        linux-mediatek@lists.infradead.org
In-Reply-To: <20200506051853.14380-1-walter-zh.wu@mediatek.com>
To:     Walter Wu <walter-zh.wu@mediatek.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On May 6, 2020, at 1:19 AM, Walter Wu <walter-zh.wu@mediatek.com> wrote:
>=20
> This patchset improves KASAN reports by making them to have
> call_rcu() call stack information. It is helpful for programmers
> to solve use-after-free or double-free memory issue.
>=20
> The KASAN report was as follows(cleaned up slightly):
>=20
> BUG: KASAN: use-after-free in kasan_rcu_reclaim+0x58/0x60
>=20
> Freed by task 0:
> save_stack+0x24/0x50
> __kasan_slab_free+0x110/0x178
> kasan_slab_free+0x10/0x18
> kfree+0x98/0x270
> kasan_rcu_reclaim+0x1c/0x60
> rcu_core+0x8b4/0x10f8
> rcu_core_si+0xc/0x18
> efi_header_end+0x238/0xa6c
>=20
> First call_rcu() call stack:
> save_stack+0x24/0x50
> kasan_record_callrcu+0xc8/0xd8
> call_rcu+0x190/0x580
> kasan_rcu_uaf+0x1d8/0x278
>=20
> Last call_rcu() call stack:
> (stack is not available)
>=20
>=20
> Add new CONFIG option to record first and last call_rcu() call stack
> and KASAN report prints two call_rcu() call stack.
>=20
> This option doesn't increase the cost of memory consumption. It is
> only suitable for generic KASAN.

I don=E2=80=99t understand why this needs to be a Kconfig option at all. If c=
all_rcu() stacks are useful in general, then just always gather those inform=
ation. How do developers judge if they need to select this option or not?=